Plasmon-Enhanced Fluorescence of EGFP on Short-Range Ordered Ag Nanohole Arrays.

Vladimir E Bochenkov,Ekaterina M Lobanova,Aleksander M Shakhov,Anastasia V Bochenkova,Artyom A Astafiev,Vadim A Timoshenko,Alexey M Bogdanov

doi:10.3390/nano10122563

Abstract

Fluorescence of organic molecules can be enhanced by plasmonic nanostructures through coupling to their locally amplified electromagnetic field, resulting in higher brightness and better photostability of fluorophores, which is particularly important for bioimaging applications involving fluorescent proteins as genetically encoded biomarkers. Here, we show that a hybrid bionanosystem comprised of a monolayer of Enhanced Green Fluorescent Protein (EGFP) covalently linked to optically thin Ag films with short-range ordered nanohole arrays can exhibit up to 6-fold increased brightness. The largest enhancement factor is observed for nanohole arrays with a propagating surface plasmon mode, tuned to overlap with both excitation and emission of EGFP. The fluorescence lifetime measurements in combination with FDTD simulations provide in-depth insight into the origin of the fluorescence enhancement, showing that the effect is due to the local amplification of the optical field near the edges of the nanoholes. Our results pave the way to improving the photophysical properties of hybrid bionanosystems based on fluorescent proteins at the interface with easily fabricated and tunable plasmonic nanostructures.

Highlights

Plasmonic nanostructures can focus light from far field sources into tiny subwavelength-scale volumes, leading to amplification of a local electric field [1]
By combining experimental and theoretical studies, we show that short-range ordered nanohole arrays in optically thin silver films, which can be fabricated on centimeter-scale supports via colloidal lithography, can be used as efficient fluorescence-enhancing substrates
We demonstrate that hybrid bionanostructures, comprised of Enhanced Green Fluorescent Proteins immobilized on perforated silver films with 120 nm apertures exhibit up to 6-fold amplified average fluorescence intensity

Summary

Introduction

Plasmonic nanostructures can focus light from far field sources into tiny subwavelength-scale volumes, leading to amplification of a local electric field [1]. Dye molecules, placed in the vicinity of a plasmonic nanostructure, can be coupled to this enhanced electric field, resulting in higher excitation and radiative decay rates, increased quantum yields and a larger number of photons emitted before photobleaching. This phenomenon is sometimes referred to as surface-enhanced fluorescence, metal-enhanced fluorescence or plasmon-enhanced fluorescence (PEF) [9,10,11,12]. It has been shown that spectral overlap between an emission band of the protein with a specific plasmon mode is important for improved fluorescence

Methods

Results

Conclusion